Milepost 31

Milepost 31

Overview

Milepost 31 is an award-winning information center that highlights the people and projects that shaped Pioneer Square, and provides an inside look at the SR 99 Tunnel Project. There, you'll find more than just construction photos and brochures. You’ll find history, artifacts and interactive exhibits designed to broaden your understanding of the land beneath you. You’ll explore the neighborhood’s changing landscape, from earth-moving efforts of the past to the massive tunnel project that will soon move State Route 99 underground and reconnect Pioneer Square to the waterfront.

Location and hours

211 First Ave. S., Seattle
Admission is free.
11 a.m. to 5 p.m. Tuesday - Saturday (closed on state holidays) 
Open until 8 p.m. on the first Thursday of each month during the Pioneer Square Art Walk - see below for details. 


Exhibit details

Visitors to Milepost 31 can browse through four sections:

You Are Here: Similar to the "you are here" points on maps, this section orients visitors to Milepost 31. It tells the story of the land upon which you are standing from the perspective for several different historical figures.

Moving Land: This section examines how the natural forces of glaciers, earthquakes and volcanoes have transformed Seattle's landscape during the past 20,000 years. Visitors will also learn about our own effects on the land, from the filling of the tidelands in Pioneer Square to the various regrade projects across the city.

Moving People: This section tracks transportation over time, with an emphasis on Pioneer Square. Visitors will see how people-moving has changed - and in some cases stayed the same.

Moving Forward: This section is all about tunneling. Visitors will learn about the history of tunneling technology, tunneling in Seattle and, of course, the SR 99 Tunnel Project. In addition, exhibits show visitors how the project - along with the Elliott Bay Seawall Replacement and Waterfront Seattle - will transform the future of Pioneer Square.

Why the name “Milepost 31”?

Mileposts mark progress. They help you track where you are on your journey, reminding you of the places you’ve passed through on your way to somewhere else.

But what if a milepost is so interesting that it becomes a destination? Located on SR 99 at the western edge of Pioneer Square, Milepost 31 is that kind of place. It marks a spot on the highway, but it also marks the spot where, before mileposts existed, mile-thick glaciers gave way to native civilizations. It’s where Seattle’s first neighborhood saw the rise of the city’s most notorious stretch of highway - the SR 99 Alaskan Way Viaduct - and where crews building the world’s largest diameter bored tunnel to replace the viaduct will first cross into the soils beneath Pioneer Square.


Events and activities 

First Thursday speaker series 

WSDOT hosts a monthly speaker series in conjunction with the First Thursday Art Walk in Pioneer Square.

Thursday, July 7 
Milepost 31, 211 First Ave. S., Seattle
Admission is free
6:00 p.m. - 6:30 p.m.

SR 99 tunnel landscaping goes back to its roots

While Bertha continues her journey from SODO to South Lake Union, trees, plants, and flowers are already growing at the finish line! Landscape architect, Katey Bean, will talk about the design of the landscape at the tunnel’s north end and how it pays homage to the indigenous landscape that used to exist in this part of Seattle.

Katey is a landscape architect and urban designer who has been working on the North Portal landscape design since 2010. She recently moved from the WSDOT landscape architecture group to HNTB, where she will continue to be involved in large infrastructure projects in and around Seattle. 

Thursday, August 4
Milepost 31, 211 First Ave. S., Seattle
Admission is free
6:00 p.m. - 6:30 p.m.

Seattle’s medieval tsunami 
 
A quarter century ago, excavations for the West Point Sewage Treatment Plant in Seattle’s Discovery Park exposed a startling find: evidence that Seattle had been hit by a tsunami sometime between the years 900 and 930 C.E. U.S. Geological Survey scientist Brian Atwater made the discovery while examining trench walls excavated as part of the construction project. Come to Milepost 31 to hear Brian recount this chance geological discovery and relate it to our region’s earthquake hazards.
 
Brian Atwater has been a U.S. Geological Survey scientist since 1974 and an affiliate faculty member at University of Washington since 1985. He has studied geologic history to clarify earthquake and tsunami hazards in California, Washington, Chile, Japan, Southeast Asia, and the Caribbean. He surveyed trench walls at West Point during construction of the plant’s main effluent pipe in 1991 and 1992.

 


Questions?

If you have questions about Milepost 31 please call the program hotline at 1-888-AWV-LINE, which is answered by staff between 8 a.m. and 5 p.m. on weekdays.

Visit Milepost 31.

 

Celebrate Seattle's past and future.

 

Come check out a model of the world's largest tunneling machine!

 

Click to sign up for a tour of tunnel construction from the viewing platform